Ver.1.0 (Updated: 110320-20:42)

Feel free to use these quotes in your stories, but please read our notes at the bottom in regards to the information here.

If you have any questions, please don't hesitate to contact us. 

* Please be aware that the comments below are in response to the information that was available at the time they were given.

Information as of March 20 01:14 JST.

 

Ritsuo Yoshioka

Mr Yoshioka is the President and CEO of the Japan Functional Safety Laboratory.  He is currently involved in training and educating about functional safety standards in Japan.
 

Why the situation will not reach recriticality at Fukushima Daiichi

 “Let me talk about a recriticality (when nuclear fission reactions keep occurring like when the power plant is operating) in terms of the nuclear reactor and the spent fuel pool.

  "For a light-water nuclear reactor to achieve criticality, three things need to happen:

1. The 1cm diameter fuel rods need to be lined up with about 1.5cm of space in between them.
2. All the fuel needs to be immersed in water.
3. The control rods need to be removed.
Unless all these conditions are met, criticality would not be achieved.
 
  "Therefore, the following is true:
  • As long as the control rods are suppressing the fuel rods, a critical situation will not occur
  • Spent nuclear fuel cannot reach criticality without water.
 
  "In regards to the spent fuel in the pool, the pool in Unit 4 is empty so criticality will not occur.  It was reported that someone had seen water inside the pool, but  Tokyo Electric Power  later clarified that it was the other pool that did not have any fuel in it.
  • The pool in Unit 3 does have water (the steam coming out is from the water) but it will not go critical, because the fuel batches are not aligned in a way to reach criticality.
It is because of these reasons that I believe a recriticality accident at Fukushima Daiichi nuclear power plant will not happen."

 

About the spread of radioactive material

  “As long as the containment vessels in Unit 1, 2, and 3 have not been damaged, radioactive material will not be released outside.   “Spent fuel has been exposed to air and has been releasing small amounts of radioactive material.  The lighter radioactive material has already been released in the form of a hydrogen gas explosion and has already spread out.  As long as there are no more explosions, it is unlikely that any more will be released.  I don’t think radiation levels will go much higher than what they are now.

  “Heavier radioactive material (such as uranium, plutonium, or cobalt, which have significant effects of humans) has been released in minute amounts, but they are so heavy that they are building up at the bottom of the pool.  As long as the situation does not reach recriticality, they will not spread out in large amounts.
 
  “A recriticality accident is unthinkable, and there is no need to worry about more radioactive material spreading than it is right now.”
 

【Notes】

・ The Science Media Centre of Japan (SMCJ) is an independent, non-profit group for the news media, giving journalists access to evidence-based science and expertise.

 Regardless of the medium, we welcome our material to be used by journalists who want to make scientific views heard in society.

 ・ The views expressed in this post are those of the individuals and organisations indicated and do not reflect the views of the SMC or its employees.

・ The SMCJ sends such information to those registered on our mailing list.  To sign up, please click on the link below.

(Please be warned that registration involves giving us some information about yourself.  Those who we think are not real journalists may be denied access to our mailing list.  This is to prevent our information from being abused, and we ask for your understanding.  However, considering the emergency we are in now, we have decided to put up all of our information publicly on this website)

  【Journalist Registration】Please contact us from HERE

 

【About this article】

○ Feel free to use these quotes in your stories.

○ In terms of crediting the SMCJ (optional), we would ask you to name is as one of the following:

  -Science Media Centre of Japan

  -Science Media Centre of Japan (Corp)

  -SMCJ

  -SMC-Japan.org

○ When sharing links, we ask that you please use: http://www.smc-japan.org

【Contact us】

○ Please contact the SMCJ with your comments on our service at:

        Science Media Centre of Japan (Corp)

  Tel/Fax: 03-3202-2514

  E-mail: inquiry[at]smc-japan.org

 

 

 

 

 

 

 

 

 

Leave a Reply

メールアドレスが公開されることはありません。 * が付いている欄は必須項目です

*

次のHTML タグと属性が使えます: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>